Ion-beam based deposition of coatings for electrochromic devices

ABSTRACT

Thin film coatings for solid state storage batteries and electrochromic energy conservation devices are now formed on low temperature glass and plastic substrates by an ion-assisted RF deposition process. The attachment of such coated glass or plastic substrates to existing windows in situ allows ordinary plate glass windows in homes, office buildings and factories to be converted to &#34;smart-windows&#34; resulting in a substantial savings in heating and air conditioning costs.

This is a divisional of application Ser. No. 405,271, filed Sep. 11,1989, now U.S. Pat. No. 5,051,274.

BACKGROUND OF THE INVENTION

"Smart-Windows" such as described in U.S. Pat. No. 4,832,463 entitled"Thin Film Ion-Conducting Coating", primarily consist of thin coatingson a transparent substrate whereby the reflective and transmissiveproperties of the electrochromic coatings can be electricallycontrolled. This Patent is incorporated herein for reference purposesand should be reviewed for its description of durable, environmentallystable materials that meet many of the automotive, aircraft and militaryperformance specifications.

A first use for such "smart-windows" is in existing buildings whereinthe expense of replacing existing plate glass windows with"smart-windows" would be prohibitably expensive.

The aforementioned U.S. Patent suggests depositing the electrochromicdevice on a flexible plastic substrate, such as mylar, which is atrademark of DuPont Company for a flexible polyester film. The provisionof the electrochromic coatings on the flexible mylar film wouldtransform ordinary windows to so called "smart-windows", when theelectrochromic mylar is attached to the interior or exterior surface ofsuch windows.

However, when electrochromic materials are deposited by conventionalvacuum deposition techniques such as thermal evaporation or RFsputtering, on to a transparent substrate for all but one of thematerials the substrate must remain at an elevated temperature in orderto control the electrical and optical properties of the device.Therefore, the use of conventional vacuum deposition techniques hasheretofore not proved feasible for conventional plastic materials sincethe plastics deteriorate when subjected to high temperatures for therequired periods of time.

Another impediment to the widespread commercialization of electrochromicsmart windows is the occurrence of pinholes and otherelectronically-shorting pathways which result from ordinary lowtemperature depositions of the middle layer, since such depositiontechniques lead to porous, low density layers.

An additional impediment to the widespread commercialization ofelectrochromic smart windows is that long deposition times are requiredto build-up the five coatings used to provide the electrochromic effect.With the method described in the aforementioned U.S. Patent, the twoouter layers must exhibit a high degree of crystallinity whereas themiddle layer must remain amorphous. The common substrate was accordinglyheated during the deposition of the first two layers, cooled during thedeposition of the third middle layer and thereafter heated during thedeposition of the final forth and fifth layers. Whereas the long heatingand cooling cycles are not conducive to commercial production, thesubstrate high temperature heating requirement eliminates mostcommercially available plastic materials.

A paper entitled "Modification of the Optical and Structural Propertiesof Dielectric ZrO₂ Film by Ion-Assisted Depositions" which appeared inthe Journal of Applied Physics, 55, January, 1984, describes theion-assisted deposition of ZrO₂ films on both heated and unheatedsubstrates. The ZrO₂ films were prepared by electron-beam evaporation ofZrO₂ accompanied by irradiation with a 600-eV argon beam. When the argonbeam was employed, the refractive index and mass density of the ZrO₂ onthe heated substrate, however, was higher than the refractive index andmass density of the ZrO₂ on the unheated substrate.

One purpose of the instant invention, accordingly, is to provide amethod for depositing high mass density electrochromic device materialsupon transparent substrates by means of a rapid deposition process thatdoes not require a heated substrate to achieve the desiredelectrochromic effects.

SUMMARY OF THE INVENTION

Electrochromic device coatings are prepared on room temperature plasticand glass transparent substrates by an RF deposition process whichincludes ion-assisted deposition. In the case of electrochromic smartwindows, the first conducting layer, counter-electrode layer, ionconducting layer, electrochromic layer and second conducting layer areeach deposited on the room temperature substrates by bombardment of thematerial accompanied by an oxygen ion beam energy of 400 electron-voltsor less.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before describing the Preferred Embodiment, it is helpful to review theteachings of the aforementioned U.S. Pat. No. 4,832,463 which describesthe composition of a five layer electrochromic energy conservation andelectronic rechargeable battery device. The first electron-conductinglayer which is directly deposited on a glass or plastic substratecomprises a tin-doped indium oxide (ITO) transparent coating to which anelectrode is attached by means of a low temperature indium metal solder.The electrochromic layer consisting of WO₃ is deposited over the ITOlayer and the ion-conducting layer of Li₂ O:Nb₂ O₅ which iselectron-resistive and ion-conductive is deposited over theelectrochromic layer. The counter-electrode layer consisting of In₂ O₃is deposited over the ion-conducting layer. A second ITO transparentcoating is deposited over the counter-electrode layer and a secondelectrode is attached to the second ITO layer by means of the lowtemperature indium metal solder. As described in the referenced U.S.Patent, the starting materials for the mixed oxide components areprepared in excess of stoichiometry such that the resulting layers arestoichiometric in composition to insure the selective ion and electrontransport properties.

In accordance with the instant invention, all five layers are preparedby a continuous deposition process within a controlled inert atmospherein which the specific mixed oxides are thermally evaporated from anelectrically heated tungsten or tantalum metal boat or from an electronbeam-heated graphite crucible. The oxides condense onto an unheatedglass substrate while simultaneously bombarding the substrate with a200-300eV oxygen beam at an incident angle varying between 0 and 80degrees. The electrochromic layer, for example, was prepared from amixture comprising 90 wt. % WO₃ and 2.5 wt. % Al₂ O₃ which was allowedto condense on the unheated coated glass substrate approximately 5-30 cmaway. The deposition was separately obtained using (a) the 200-300eVoxygen beam (b) the 200-300eV argon beam (c) no beam during deposition.The electrochromic layer was also deposited on a Mylar plastic film. Theresults showed that by using the 200-300eV oxygen beam the WO₃ filmexhibited good transparency and readily colored upon ion-insertion withcorresponding measured high near-infrared reflectance. The WO₃ filmformed with the 200-300eV argon beam or no beam at all appeared to bechemically reduced and hence visibly colored. X-ray diffractionmeasurements for such depositions exhibited no crystallinity whilelithium-insertion produced no increase in free electron near-infraredadsorbtion or reflection which is a measure of the degree ofelectrochromic activity.

On the other hand, the WO₃ film formed with the 200-300eV oxygen beamwas visibly transparent, and X-ray diffraction measurements for suchdepositions indicated that the films were crystalline, and lithiuminsertion produced a marked increase in near-infrared reflection, thusindicating a high degree of desirable electrochromic activity.Furthermore, such depositions exhibited higher mass densities than whenno energetic beam of argon or oxygen was used.

Having thus described our invention, what we claim as new and desire toseek by Letters Patent is:
 1. An electrochromic device comprising:alight transmissive substrate having a first layer ofelectrically-conductive material deposited thereon by thermalevaporation; a layer of tungsten oxide deposited on said first layer bythermal evaporation of tungsten oxide within a stream of oxygen or argonions; a layer of ion conductive-electron resistive material deposited onsaid tungsten oxide by thermal evaporation; a counter-electrode layerdeposited on said electron resistive-ion conductive layer by thermalevaporation; and a second layer of electrically-conductive material onsaid counter-electrode layer by thermal evaporation.
 2. Theelectrochromic device of claim 1 wherein said light-transmissivesubstrate comprises plastic or glass.
 3. The electrochromic device ofclaim 1 wherein said first and second electrically-conductive materialscomprise indium and tin oxides.
 4. The electrochromic device of claim 1wherein said ion conductive-electron resistive layer comprises alithiated oxide.
 5. The electrochromic device of claim 1 wherein saidcounter-electrode layer comprises indium oxide.